1. Field of the Invention
The present invention relates to a capacitor comprising a lower electrode, an upper electrode layer, and a dielectric layer disposed between the lower electrode and the upper electrode layer, and to a method of manufacturing such a capacitor.
2. Description of the Related Art
With increasing demands for reductions in dimensions and thickness of high frequency electronic apparatuses such as cellular phones, reductions in dimensions and height of electronic components mounted on the high frequency electronic apparatuses have been sought. One of the electronic components is a capacitor. The capacitor typically incorporates a dielectric layer and a pair of electrode layers disposed to sandwich the dielectric layer.
To achieve reductions in dimensions and height of a capacitor, important factors are a reduction in area of a region in which the pair of electrode layers are opposed to each other with the dielectric layer disposed in between and a reduction in the number of layers making up the capacitor. To achieve these, it is effective to reduce the thickness of the dielectric layer. A capacitor incorporating a dielectric layer formed through thin-film forming techniques such as sputtering (such a capacitor may be hereinafter called a thin-film capacitor), as disclosed in Japanese Published Patent Application 2002-26266, for example, is known as being capable of achieving a reduction in thickness of the dielectric layer. The capacitor disclosed in this publication is formed by stacking a first electrode layer, a dielectric layer and a second electrode layer in this order on a base substrate.
As disclosed in this publication, conventional thin-film capacitors have a problem that, if the thickness of the dielectric layer is reduced, leakage current of the dielectric layer is increased and/or the withstand voltage of the dielectric layer is reduced. It is assumed that this problem results from pinholes and crystal grain boundaries existing in the dielectric layer, as disclosed in the above-mentioned publication.
To solve this problem, the above-mentioned publication discloses a technique in which an insulator formed by oxidizing the material of the first electrode layer is provided in part between the first electrode layer and pinholes or grain boundaries of the dielectric layer.
The inventors of the present patent application conceived a method of manufacturing a thin-film capacitor by stacking a dielectric layer and an upper electrode layer one by one through thin-film forming techniques on a metallic foil that functions as both of a substrate and a lower electrode. According to this technique, it is possible to mass-produce thin-film capacitors at lower costs, compared with the case of manufacturing a thin-film capacitor by stacking a lower electrode layer, a dielectric layer and an upper electrode layer one by one on a substrate through thin-film forming techniques.
However, in the thin-film capacitors manufactured by stacking the dielectric layer and the upper electrode layer on the metallic foil through thin-film forming techniques as described above, a short-circuit failure and/or an increase in leakage current of the dielectric layer has been found to occur in some cases even if the dielectric layer has no defect. Such a phenomenon has not been experienced in thin-film capacitors manufactured by stacking a lower electrode layer, a dielectric layer and an upper electrode layer on a substrate through thin-film forming techniques.
As disclosed in Japanese Published Patent Application 2002-26266, it is known that an increase in leakage current of the dielectric layer and a reduction in withstand voltage of the dielectric layer can occur due to defects existing in the dielectric layer. However, there has been no recognition that a short-circuit failure and/or an increase in leakage current of the dielectric layer can occur even if the dielectric layer has no defect.
In a case in which an insulator is provided on or below a part of the dielectric layer in a thin-film capacitor to prevent the occurrence of short-circuit failure and an increase in leakage current of the dielectric layer, if the insulator is too large, the characteristics of the capacitor may be degraded due to the existence of the insulator.